These procedures manage a collection of cursors
being used by an application. The procedures allow cursors to be
re-used efficiently, thereby avoiding server overhead, and also
allow cursors to be named with character strings.

Tk_AllocCursorFromObj takes as argument an object describing a
cursor, and returns an opaque Tk identifier for a cursor corresponding
to the description. It re-uses an existing cursor if possible and
creates a new one otherwise. Tk_AllocCursorFromObj caches
information about the return value in objPtr, which speeds up
future calls to procedures such as Tk_AllocCursorFromObj and
Tk_GetCursorFromObj. If an error occurs in creating the cursor,
such as when objPtr refers to a non-existent file, then None
is returned and an error message will be stored in interp's result
if interp is not NULL. ObjPtr must contain a standard Tcl
list with one of the following forms:

Name is the name of a cursor in the standard X cursor cursor,
i.e., any of the names defined in cursorcursor.h, without
the XC_. Some example values are X_cursor, hand2,
or left_ptr. Appendix B of
“The X Window System”
by Scheifler & Gettys has illustrations showing what each of these
cursors looks like. If fgColor and bgColor are both
specified, they give the foreground and background colors to use
for the cursor (any of the forms acceptable to Tk_GetColor
may be used). If only fgColor is specified, then there
will be no background color: the background will be transparent.
If no colors are specified, then the cursor
will use black for its foreground color and white for its background
color.

The Macintosh version of Tk supports all of the X cursors and
will also accept any of the standard Mac cursors
including ibeam, crosshair, watch, plus, and
arrow. In addition, Tk will load Macintosh cursor resources of
the types crsr (color) and CURS (black and white) by the
name of the resource. The application and all its open
dynamic library's resource files will be searched for the named
cursor. If there are conflicts color cursors will always be loaded
in preference to black and white cursors.

In this form, sourceName and maskName are the names of
files describing cursors for the cursor's source bits and mask.
Each file must be in standard X11 cursor format.
FgColor and bgColor
indicate the colors to use for the
cursor, in any of the forms acceptable to Tk_GetColor. This
form of the command will not work on Macintosh or Windows computers.

This form is similar to the one above, except that the source is
used as mask also. This means that the cursor's background is
transparent. This form of the command will not work on Macintosh
or Windows computers.

This form only works on Windows, and will load a Windows system
cursor (.ani or .cur) from the file specified in
sourceName.

Tk_GetCursor is identical to Tk_AllocCursorFromObj except
that the description of the cursor is specified with a string instead
of an object. This prevents Tk_GetCursor from caching the
return value, so Tk_GetCursor is less efficient than
Tk_AllocCursorFromObj.

Tk_GetCursorFromObj returns the token for an existing cursor, given
the window and description used to create the cursor.
Tk_GetCursorFromObj does not actually create the cursor; the cursor
must already have been created with a previous call to
Tk_AllocCursorFromObj or Tk_GetCursor. The return
value is cached in objPtr, which speeds up
future calls to Tk_GetCursorFromObj with the same objPtr
and tkwin.

Tk_GetCursorFromData allows cursors to be created from
in-memory descriptions of their source and mask cursors. Source
points to standard cursor data for the cursor's source bits, and
mask points to standard cursor data describing
which pixels of source are to be drawn and which are to be
considered transparent. Width and height give the
dimensions of the cursor, xHot and yHot indicate the
location of the cursor's hot-spot (the point that is reported when
an event occurs), and fg and bg describe the cursor's
foreground and background colors textually (any of the forms
suitable for Tk_GetColor may be used). Typically, the
arguments to Tk_GetCursorFromData are created by including
a cursor file directly into the source code for a program, as in
the following example:

Under normal conditions Tk_GetCursorFromData
will return an identifier for the requested cursor. If an error
occurs in creating the cursor then None is returned and an error
message will be stored in interp's result.

Tk_AllocCursorFromObj, Tk_GetCursor, and
Tk_GetCursorFromData maintain a
database of all the cursors they have created. Whenever possible,
a call to Tk_AllocCursorFromObj, Tk_GetCursor, or
Tk_GetCursorFromData will
return an existing cursor rather than creating a new one. This
approach can substantially reduce server overhead, so the Tk
procedures should generally be used in preference to Xlib procedures
like XCreateFontCursor or XCreatePixmapCursor, which
create a new cursor on each call. The Tk procedures are also more
portable than the lower-level X procedures.

The procedure Tk_NameOfCursor is roughly the inverse of
Tk_GetCursor. If its cursor argument was created
by Tk_GetCursor, then the return value is the name
argument that was passed to Tk_GetCursor to create the
cursor. If cursor was created by a call to Tk_GetCursorFromData,
or by any other mechanism, then the return value is a hexadecimal string
giving the X identifier for the cursor.
Note: the string returned by Tk_NameOfCursor is
only guaranteed to persist until the next call to
Tk_NameOfCursor. Also, this call is not portable except for
cursors returned by Tk_GetCursor.

When a cursor returned by Tk_AllocCursorFromObj, Tk_GetCursor,
or Tk_GetCursorFromData
is no longer needed, Tk_FreeCursorFromObj or
Tk_FreeCursor should be called to release it.
For Tk_FreeCursorFromObj the cursor to release is specified
with the same information used to create it; for
Tk_FreeCursor the cursor to release is specified
with its Tk_Cursor token.
There should be exactly one call to Tk_FreeCursor for
each call to Tk_AllocCursorFromObj, Tk_GetCursor,
or Tk_GetCursorFromData.

In determining whether an existing cursor can be used to satisfy
a new request, Tk_AllocCursorFromObj, Tk_GetCursor,
and Tk_GetCursorFromData
consider only the immediate values of their arguments. For
example, when a file name is passed to Tk_GetCursor,
Tk_GetCursor will assume it is safe to re-use an existing
cursor created from the same file name: it will not check to
see whether the file itself has changed, or whether the current
directory has changed, thereby causing the name to refer to
a different file. Similarly, Tk_GetCursorFromData assumes
that if the same source pointer is used in two different calls,
then the pointers refer to the same data; it does not check to
see if the actual data values have changed.